Systems and methods for nerve mapping and monitoring

ABSTRACT

Embodiments can include a nerve mapping and monitoring system that can include a multi-polar stimulation unit, an electrical connector, an instrument having a grid array, where the grid array can comprise a plurality of electrodes, where each of the plurality of electrodes can be configured to be stimulated by the multi-polar stimulation unit, a recording element, where the recording element can be configured to detect a muscle response elicited by the grid array, and a computer, where the computer can be configured to monitor the muscle response elicited by the grid array such that neural structures can be identified and avoided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/025,249, filed Jul. 2, 2018, which application is a continuation ofU.S. patent application Ser. No. 14/059,256, filed Oct. 21, 2013, whichapplication claims the priority benefit of U.S. Provisional PatentApplication No. 61/715,956, filed Oct. 19, 2012. The disclosures of eachof the foregoing applications are hereby incorporated by referenceherein in their entireties.

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

TECHNICAL FIELD

Embodiments of the technology relate, in general, to systems and methodsfor intraoperative peripheral nerve motor fiber mapping and monitoring,and in particular to systems and methods for intraoperative peripheralnerve motor fiber mapping and monitoring that can be applied to avariety of surgical instruments including but not limited to surgicalprobes, tissue dilators, and retractors.

BACKGROUND

Many types of nerve injury can be caused during surgical procedures,where such nerve damage can have long lasting or permanent effects. Manysurgical procedures come into close contact with neural structures andthese procedures have the potential to permanently harm or even killpatients. In addition to other neural damage, neurapraxia, axonotmesis,or neurotmesis can result from surgical procedures.

SUMMARY

Embodiments can include a nerve mapping and monitoring system that caninclude a multi-polar stimulation unit, an electrical connector that canhave a first end and a second end, where the first end can be coupledwith the multi-polar simulation unit, an instrument having a grid array,where the grid array can comprise a plurality of electrodes, where eachof the plurality of electrodes can be configured to be stimulated by themulti-polar stimulation unit, a recording element, where the recordingelement can be configured to detect a muscle response elicited by thegrid array, and a computer system, where the computer system can beconfigured to monitor the muscle response elicited by the grid arraysuch that neural structures can be identified and avoided.

Embodiments can include a nerve mapping and monitoring system that caninclude a multi-polar stimulation unit, an electrical connector that canhave a first end and a second end, wherein the first end is coupled withthe multi-polar simulation unit, a ring connector, wherein the ringconnector can be coupled with the second end of the electricalconnector, an instrument having a first end and a second end, theinstrument including a lower portion and an upper portion divided by ahorizontal circumferential line, where the ring connector can beconfigured for attachment to the upper portion of the instrument, a gridarray, where the grid array can be positioned on the lower portion ofthe instrument, where the grid array can comprise a plurality ofelectrodes that can be circumferentially positioned about the lowerportion of the instrument, where each of the plurality of electrodes cancomprise an alphanumeric notation and can be configured to be stimulatedindependently by the multi-polar stimulation unit. The nerve mapping andmonitoring system can include a recording element, where the recordingelement can be configured to detect a muscle response elicited by thegrid array, a computer system, where the computer system can beconfigured to monitor the muscle response elicited by the grid arraysuch that neural structures can be identified and avoided, and adisplay, where the display can be configured to visually represent theresponse elicited by the grid array and monitored by the computersystem.

Embodiments can include a nerve mapping and monitoring system that caninclude a means of generating multi-polar stimulation, a means fordelivering multi-polar stimulation to a patient, a means for detectingthe patient's muscle response to the multi-polar stimulation, and meansfor determining the location of neural structures based upon thepatient's muscle response.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be more readily understood from a detaileddescription of some example embodiments taken in conjunction with thefollowing figures:

FIG. 1 depicts an example nerve monitoring and mapping system accordingto one embodiment.

FIG. 2A depicts a front perspective view of a handheld surgical probeand connector of a wiring system according to one embodiment.

FIG. 2B depicts a rear perspective view of the handheld surgical probeshow in FIG. 2A.

FIG. 3A depicts a partial magnified view of the handheld surgical probeshown in FIG. 2A.

FIG. 3B depicts a partial magnified view of the handheld surgical probeshown in FIG. 2B.

FIG. 4 depicts front perspective view of a surgical probe and aperspective view of an associated wiring system according to oneembodiment.

FIG. 5A depicts a front perspective view of a surgical probe associatedwith an electrical ring connector according to one embodiment.

FIG. 5B depicts a partial magnified view of the electrical ringconnector shown in FIG. 5A.

FIG. 6A depicts a front perspective view of surgical probe according toone embodiment.

FIG. 6B depicts a front perspective view of surgical probe according toan alternate embodiments.

FIG. 6C depicts a front perspective view of the surgical probe shown inFIG. 5A.

FIG. 7A depicts a font perspective view of a surgical sequentialdilation system that can fit multiple tube dilators over one another tosequentially create a surgical corridor according to one embodiment.

FIG. 7B depicts a front perspective view of the surgical sequentialdilation system shown in FIG. 7A shown in association with a multi-polarstimulation unit.

FIG. 8 depicts a front perspective view of an electrical ring connectorassociated with a surgical probe according to one embodiment.

FIG. 9A depicts a front perspective view of a surgical probe associatedwith an electrical ring connector and a perspective view of anassociated wiring system according to one embodiment.

FIG. 9B depicts a partial magnified view of the electrical ringconnector shown in FIG. 9A.

FIG. 10 depicts a front perspective view of a retractor system that canbe fitted with a multi-polar grid electrode system according to oneembodiment.

FIG. 11A depicts a front perspective view of the multi-polar gridelectrode system shown in FIG. 10 according to one embodiment.

FIG. 11B depicts a cross-sectional view of the multi-polar gridelectrode system shown in FIG. 11A according to one embodiment.

FIG. 11C depicts a partial magnified view of the multi-polar gridelectrode system shown in FIG. 11B.

FIG. 12 depicts a front perspective view of a multi-polar grid electrodesystem have alphanumeric assignments according to one embodiment.

FIG. 13 depicts a front perspective view of a display for a systemaccording to one embodiment.

FIG. 14A depicts a front perspective view of a multi-polar surgicalprobe associated with a multi-polar sequential dilation system and amulti-polar surgical retractor system according to one embodiment.

FIG. 14B depicts a front perspective view of the multi-polar surgicalprobe, the multi-polar sequential dilation system, and the multi-polarsurgical retractor system of FIG. 14A, shown in an alternateconfiguration.

FIG. 15A depicts a front perspective view of a stimulation systemaccording to one embodiment shown with alphanumeric electrodedesignations.

FIG. 15B depicts a front perspective view of the stimulation system ofFIG. 15A, shown indicating a mono-polar response.

FIG. 15C depicts a front perspective view of the stimulation system ofFIG. 15A, shown indicating a first bi-polar response.

FIG. 15D depicts a front perspective view of the stimulation system ofFIG. 15A, shown indicating a second bi-polar response.

FIG. 16A depicts a front perspective view of a bi-polar stimulationsystem according to one embodiment shown with alphanumeric electrodedesignations.

FIG. 16B depicts a front perspective view of the bi-polar stimulationsystem of FIG. 16A, shown indicating a first response.

FIG. 16C depicts a front perspective view of the bi-polar stimulationsystem of FIG. 16A, shown indicating a second response.

FIG. 17A depicts a front perspective view of a tri-polar stimulationsystem according to one embodiment shown with alphanumeric electrodedesignations.

FIG. 17B depicts a front perspective view of the tri-polar stimulationsystem of FIG. 17A, shown indicating a first response.

FIG. 17C depicts a front perspective view of the tri-polar stimulationsystem of FIG. 17A, shown indicating a second response.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various non-limiting embodiments of the present disclosure will now bedescribed to provide an overall understanding of the principles of thestructure, function, and use of the proficiency tracking systems andprocesses disclosed herein. One of more examples of these non-limitingembodiments are illustrated in the accompanying drawings. Those ofordinary skill in the art will understand that systems and methodsspecifically described herein and illustrated in the accompanyingdrawings are non-limiting embodiments. The features illustrated ordescribed in connection with one non-limiting embodiment may be combinedwith the features of other non-limiting embodiments. Such modificationsand variations are intended to be included within the scope of thepresent disclosure.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” “some example embodiments,” “one exampleembodiment,” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with any embodimentis included in at least one embodiment. Thus, appearances of the phrases“in various embodiments,” “in some embodiments,” “in one embodiment,”“some example embodiments,” “one example embodiment,” or “in anembodiment” in places throughout the specification are not necessarilyall referring to the same embodiment. Furthermore, the particularfeatures, structures or characteristics may be combined in any suitablemanner in one or more embodiments.

Described herein are example embodiments of nerve mapping and monitoringsystems and methods that can improve the safety of surgical procedures.In one example embodiment, the system can map peripheral nerves byelectrically exciting a nerve or nerve root with stimulating electrodeswhile simultaneously recording the evoked response of the resultantelectrical activity from the muscles that are innervated. In someembodiments, the electrical activity can be recorded with surface padsthat can be placed on a patient's skin in close proximity to the musclesof interest.

The examples discussed herein are examples only and are provided toassist in the explanation of the apparatuses, devices, systems andmethods described herein. None of the features or components shown inthe drawings or discussed below should be taken as mandatory for anyspecific implementation of any of these the apparatuses, devices,systems or methods unless specifically designated as mandatory. For easeof reading and clarity, certain components, modules, or methods may bedescribed solely in connection with a specific figure. Any failure tospecifically describe a combination or sub-combination of componentsshould not be understood as in indication that any combination orsub-combination is not possible. Also, for any methods described,regardless of whether the method is described in conjunction with a flowdiagram, it should be understood that unless otherwise specified orrequired by context, any explicit or implicit ordering of stepsperformed in the execution of a method does not imply that those stepsmust be performed in the order presented but instead may be performed ina different order or in parallel.

Example embodiments described herein can assist surgeons in safelyaccessing deep surgical sites while preventing or minimizing the chancethat neurological structures are damaged. For example, an operativecorridor can be created that can reduce or prevent the likelihood thatneurological damage will occur.

A nerve mapping and monitoring computer system can execute software forthe operation of a surgical probe and related systems, as described inmore detail below. The nerve mapping and monitoring computer system canrun on any suitable computing system, such as a dedicated serve, a usercomputer or server, multiple computers, a collection of networkedcomputers, a cloud-based computer system, a web-based computer system,or from a storage device, for example. One or multiple processing units,such as central processing units and/or graphics processing units, mayperform instructions stored in memory to execute the processes describedtherein.

A nerve mapping and monitoring computer system in accordance with thepresent disclosure can be accessed via any suitable technique, such as aweb-browser such as SAFARI, OPERA, GOOGLE CHROME, INTERNET EXPLORER, orthe like executing on a client device. In some embodiments, the systemsand methods described herein can be a web-based application or astand-alone executable. Additionally, in some embodiments, the systemsand methods described herein can integrate with various types of nervemapping and monitoring systems, such as multi-polar stimulation probestissue dilator systems, wiring systems, mono-polar system, bi-polarsystems, needle electrodes, surface pads, tri-polar systems, and thelike. Any suitable client device can be used to access, or execute, thenerve mapping and monitoring computer systems computing system, such aslaptop computers, desktop computers, smart phones, tablet computers,gaming system, and the like.

Systems and methods described herein may generally provide a safeenvironment for users (e.g., surgeons) to perform surgical procedureswith a reduced risk of neurological damage. Interaction with the nervemapping and monitoring system may include, without limitation, keyboardentry, writing from pen, stylus, finger, or the like, with a computermouse, or other forms of input (voice recognition, etc.). Theinformation or data related to the mapping or monitoring may bepresented on a tablet, desktop, phone, board, or paper, or in anysuitable manner. In one embodiment, the user may interact with a mappingand monitoring system by writing with a smart pen on normal paper,modified paper, or a hard flat surface or their preference. In thisembodiment, the user may receive real-time feedback, or at least nearreal-time feedback, or may synchronize with a nerve mapping andmonitoring computer system at a later date. The nerve mapping andmonitoring computer system can include a personal computer, one ormultiple computers in server-type system, or any other suitablearrangement.

User interaction with the nerve mapping and monitoring computer systemmay take place in any of a variety of operational environments, such asa hospital setting or clinical setting, with one or more usersinteracting with the system at a given time. Versions describe hereininclude systems and methods for intraoperative peripheral nerve motorfiber mapping and monitoring which can be applied to a variety ofsurgical instruments including but not limited to surgical probes,tissue dilators, and retractors. Such systems and methods can provide asurgeon with useful information intraoperatively including alerting thesurgeon to the presence of neural structures in a surgical field,providing information about the relative direction and location ofneural structures in the surgical field, provide quantitative estimatesof the proximity of neural structures in relation to the surgicalequipment, and providing continuous monitoring of the function of neuralstructures in the surgical field.

Versions described herein can be aimed at assisting surgeons inproviding safer surgery for a variety of procedures that can involvecreating an operative corridor from the skin surface to a given deepsurgical target site. Creation and maintenance of a surgical corridorcan involve passing in close proximity to various neural structures.Damage to these neural structures can result in post-operativeneurological impairments which may range from mild transient motor andsensory disturbances to severe, permanent motor paralysis and/orpost-operative intractable pain or paresthesias. Prevention ofneurological damage in surgery is important as the consequences of thesecomplications can be devastating to patients and costly and difficult totreat post-operatively. Embodiments described herein can assist thesurgeon in safely accessing deep surgical sites while preventing damageto neurological structures. Versions described herein can improve theresolution and accuracy of neurophysiological recordings compared toexisting systems and methods of intraoperative nerve mapping andmonitoring and can increase the surface area of the operative corridorwhich can be monitored and protected.

Neuromonitoring and mapping of peripheral nerves can includeelectrically exciting a nerve/nerve root with stimulating electrodes(such as a single anode and cathode) while simultaneously recording theevoked response of the resultant electrical activity from the muscle(s)that are innervated by that nerve with standard electromyographytechniques. Recording of the evoked responses can be performed with, forexample, surface pads on the skin over the muscle or with needleelectrodes embedded within or in close proximity to the muscle ormuscles of interest.

With electrical stimulation of a peripheral nerve/nerve root, theminimal amount of electrical current required to elicit a muscleresponse can be termed the “motor threshold” (which can be measured inmilliamps). The act of determining the minimum amount of current toelicit a motor response in a gen muscle is generally termed “motorresponse thresholding”. Motor thresholding can help make quantitativeestimates of the proximity of motor nerve fibers in the surgical fieldbased on the amount of current delivered to the stimulating electrodes(measured in milliamps). The theory is based on the generally acceptedpremise that the motor threshold is directly proportional to theproximity of the stimulating electrodes to the nervous tissue. In otherwords, the lower the amount of current required to elicit a motorresponse, the closer the stimulating electrodes are to the nerve. Forexample, a motor threshold response in a given muscle from electricalstimulation at 2 mA of current can suggest that the stimulatingelectrodes are in closer proximity to a nerve in comparison to a motorthreshold response at 12 mA.

Embodiments described herein can include a software driven electricalstimulation system that can deliver precisely controlled electricalstimulation to various combinations of electrodes that can be located ona grid array of electrodes fixed on to various types of surgicalequipment such as, for example, a probe, tissue dilator, retractor, orthe like. The grid array of electrodes, whether in a wand-like probe,cylindrical shaped probe, or incorporated into retractor blades, canafford accurate and precise monitoring in three-dimensional spacethroughout the depth and surface(s) of soft and hard anatomicalstructures (e.g., muscle such as psoas, brain tissue). A computer candirect an external electrical power source to systematically providecontrolled, focal electrical stimulation sequentially to varying sets ofelectrodes on the grid. Any electrically evoked muscle responses fromeach of the sets of electrodes can be recorded and the amount ofelectrical current required to elicit each muscle response can beobtained with standard electromyography (EMG) techniques. A display ofthe results can alert a surgeon to the presence of neural structures inrelation to each particular electrode on the grid (mapping). Inaddition, the amount of stimulation required to elicit a response (motorthreshold) of each set of electrodes can provide quantitative estimatesabout the proximity of the electrodes on the grid to each specificelectrode on the grid. A color coded virtual “map” of these thresholdvalues can be displayed to illustrate the presence, proximity, and/ordirection of neural structures in the surgical field in relation to thesurgical equipment.

In addition, the functional status of neurological structuresencountered in the surgical field can be obtained throughout theduration of the procedure (neuromonitoring). Changes in thecharacteristics of the electrically evoked motor responses (as comparedto baseline values) can alert the surgeon of possible impendingneurological damage. Such changes in the evoked muscle responses withperipheral nerve/root electrical stimulation are described in varioustexts and are commonly utilized in intraoperative peripheral nervemonitoring. Examples of these variables may include changes in theevoked muscle response morphology, latency, slope and the amount ofcurrent required to elicit a response.

Referring now to FIG. 1, one embodiment a nerve mapping and monitoringsystem 10 is shown. The nerve mapping and monitoring system 10 can becontrolled by specifically designed software controlled by a laptop orcomputer 12. The computer 12 can be connected to a differentialamplifier or main control box 14 which can be built specifically forthis purpose or the system can be used with an existing commerciallyavailable differential amplifier. If this system is utilized with anexisting commercially available differential amplifier, additionalsoftware can be provided that can allow for utilization of a multi-polarstimulation unit 16. The multi-polar stimulation unit 16 can providesoftware controlled electrical stimulation independently, for example,to each electrode on the grid of any surgical instrument fitted with amulti-polar electrical grid. Such instruments can include, but are notlimited to, a surgical probe 18, a tissue dilator 20 or a retractorsystem 22. Different grid layouts can be applied to each specific pieceof surgical equipment and the software controlling the electricalstimulation and recording can be specifically programmed for eachparticular grid.

A patient 24 can be fitted with a recording needle or surface electrodes26 in multiple muscles of interest. The recording electrodes 26 can beconnected to a pre-amplifier 29 such as is commonly used inintraoperative EMG recording systems. The pre-amplifier 29 can beconnected to the main base unit containing a differential amplifier ormain control box 14 that can integrate the EMG recordings with theelectrical stimulation.

The software can be designed to control the multi-polar stimulation unit16 to sequentially deliver precise amounts of electrical current tovarying sets of electrodes on the grid while simultaneously recordingany motor responses with the pre-amplifier 29 and main control box 14with standard electromyography recording techniques. The software can bedesigned to detect the presence of any muscle responses recordedfollowing each electrical stimulation. Sequential electricalstimulations of varying sets of electrodes on the grid can illustratewhich sets of electrodes elicit motor responses and which sets ofelectrodes do not. The lowest level of electrical stimulation requiredto obtain a motor response from each set of electrodes can be recorded(e.g., the motor threshold level). Once this information is obtainedfrom multiple stimulations of multiple sets of electrodes on the grid,the software can generate a color coded map, or other visual display, ofthe grid correlating to the levels of electrical stimulation required toelicit motor responses from each electrode. A virtual representation ofthe grid can be displayed for the surgeon to view on a monitor 28. The“virtual map” can provide vital information to assist the surgeon innavigating around neural structures and thus avoiding damage.

The presence of absence of electrically evoked motor responses fromstimulation of sets of electrodes on the grid can be recorded, colorcoded, and presented on monitor 28. Evoked muscle responses generated atlow electrical stimulation levels (low threshold responses) can be colorcoded as progressively darker shades of red, signifying a warning ofclose proximity to neural structures. Motor responses evoked atrelatively higher stimulation levels can be designated in shades ofyellow signifying caution relating to the presence of neural structuresnear the specific stimulating electrodes on the grid. Absent motorresponses at even higher stimulation levels can be color coded as greensignifying an absence of motor neural structures in proximity to thespecific electrodes on the grid. This “traffic light” color codingsystem can be utilized to inform the surgeon of the presence and/orproximity of neural structures in relation to each electrode on the gridand can help create a useful navigational map of the surgical field. Itwill be appreciated that any suitable visual, tactile, and/or auditorydisplay or feedback is contemplated. The actual stimulation thresholdlevels (which can be measured in mA) that evoke motor responses that areto be designated by the software to be displayed as red, yellow orgreen, can be based on the relative motor threshold values obtained invivo, or the threshold values that correlate to a particular color canbe pre-programmed based on clinical experience or the results ofexperimental studies, such as animal models.

In some embodiments, referring to FIG. 13, the monitor 28 can displaythe results of a multi-polar threshold sequencing run with a multi-polarplanar grid on a retractor blade. The lowest threshold electricallyevoked motor responses can be seen with electrical stimulationsinvolving electrode #1A. In this example, motor evoked responses fromstimulation with electrode #1A are observed in the vastus lateralis andvastus medialis muscles at 8.6 mA and 8.3 mA respectively.

The example of a virtual map can provide important information to thesurgeon including informing the surgeon of the presence of neuralstructures in the surgical field or giving the surgeon an idea of whichparticular neural structures are present. In this example, it is likelythat the retractor is near the lumbar nerve roots (L2, L3, or L4) or thefemoral nerve. The nerve mapping and monitoring system 10 can provideinformation regarding the direction of neural structures in the field(nearest to the left distal tip of the retractor), can give informationregarding the relative proximity of a retractor to the neural structureas evidenced by the relatively low amount of current (8.3-8.6 mA)required to elicit a threshold motor response, and can provideinformation illustrating an absence of detectable motor nerve fibers inproximity of the remainder of the retractor blade surface (green areas).

FIGS. 2A and 2B depict a version of a handheld surgical probe 18 thatcan be made of an electrically insulating material and can be fittedwith a grid 30 of electrodes. The grid 30 of electrodes can be arrangedcircumferentially around the probe with equidistant spacing between theelectrode surfaces. The optimal number, size, shape and configuration ofthe electrodes on the grid can vary according to the particular surgicalrequirements. The optimal electrode configuration may be determinedexperimentally or by mathematical modeling, for example.

A horizontal circumferential line 32 can separate the handle area 34located above the line where a surgeon can safely touch and maneuver theprobe surgical probe 18. An effective electrical stimulation area 36 cancontain the grid 30 of electrodes and can be located below thehorizontal circumferential line 32. An electrical pin connector 38 canconnect the external multi-polar stimulation unit 16 to the electricalcontact ports located at the top of the surgical probe 18. An anteriororientation line 40, can provide a reference point on the probe relativeto the surgical field. The anterior orientation line could be coloredfor contrast for easy recognition within in the surgical field. Theanterior orientation line 40 can be considered to be at a “12 o'clockposition” or considered “north” to designate its relative position inthe surgical field. A posterior orientation line 42, which can becolored differently to distinguish it from the anterior orientation line40, can be placed in a position 180° from the anterior orientation line40. This posterior orientation line 42 can be considered to be locatedat a “6 O'clock” position or “south” relative to the surgical field.

Referring to FIGS. 3A and 3B, an example of the configuration andnomenclature of a circumferential electrode grid 30 on a surgical probe18 is shown. The grid 30 of stimulating electrodes can be placed, forexample, equidistantly and circumferentially around the surgical probe18 to obtain an effective 360° of stimulating surface along the lengthof the effective electrical stimulation area 36 of the surgical probe18. Electrodes 31 in the grid 30 can be designated with alphanumericnames by their orientation on the probe depending on their position oneach column and row of the grid.

In one version, the designation of alphanumeric names of each particularelectrode 31 can direct the software to control the delivery ofprecisely controlled electrical stimulation from the multi-polarstimulation unit 16 independently to each electrode 31 on the grid 30 asis described in greater detail with reference to multi-polar electricalstimulation sequencing of peripheral nerves/roots with sequential motorthresholding using circumferential and planar grid arrays.

As illustrated in FIGS. 3A and 3B, rows or the vertical positions ofelectrodes 31 can be numbered starting with #1 at the most distal tip ofthe surgical probe 18. In the example configuration provided, there are8 rows with the #1 electrode at the most distal tip of the surgicalprobe 18 with subsequent numbering of the rows of electrodes continuingupward with the row #8 electrodes 31 being located at the uppermostportion of the stimulating area 36 of the surgical probe 18. The actualnumber of stimulating electrodes 31 on any given grid 30 can varyaccording to particular surgical requirements. For an electrifiedsurgical probe, it may be advantageous to have only a single electrodeat the distal tip however different electrode configurations may befound to be more effective.

The columns or horizontal positions of electrodes can be letteredstarting with the “A” electrode of each column located directly on themiddle of the colored anterior orientation line 40. Subsequentelectrodes in each column can be designated alphabetically in aclockwise direction around the circumference of the surgical probe 18for each column. In the example illustration provided, each column(except for row 1) has 4 electrodes named A, B, C, and D, sequentiallydesignated in a clockwise direction. In this illustration, the “A”electrode in each column is located on the anterior orientation line 40.The A electrode can be also referred to as the “North” electrode. The“B” electrode in each column is located 90° clockwise to the “A”electrode at a 3 o'clock position (or referred to as the “East”electrode). The “C” electrode in each column is located 180° from the“A” electrode on the posterior orientation 42 (which could be coloreddifferently than the anterior orientation line 40). The posteriororientation line 42 can designate a “6 o'clock” or a “South” position.The “D” electrode in each column is located in a position 270° clockwisefrom the “A” electrode (located at 9 O'clock or considered “West”).These references to a clock or a compass are common ways of assisting indirectional orientation and can be helpful to assist the surgeon toquickly comprehend the relative location of neural structures within thesurgical field relative to the anterior orientation line 40.

In the illustrated example, a twenty-nine electrode 31 grid 30 montageon a circumferential multi-polar surgical probe 18 is shown. Thenomenclature for each electrode can contain a designation of the row (1,2, 3, 4, 5, 6, 7 and 8) (numbered from the distal tip of the probetowards the top) and can be followed by a designation of the column (A,B, C & D) (lettered alphabetically clockwise from the anteriororientation line). It will be appreciated that any suitable electrodeorientation, any suitable electrode number, and any suitablenomenclature, marking, or identifying is contemplated.

Referring to FIG. 4, one version of an electrical grid 44 is shown thatcan be wired on the multi-polar surgical probe 18. Each electrode 31 canbe wired with wires 46 directly and independently of the otherelectrodes to provide precisely controlled, focal electrical stimulationto each electrode 31 on the grid 30. An electrical pin connector 38 canconnect the external multi-polar stimulating unit 16 to the electricalcontact connector ports 48 located at the top of the surgical probe 18.It will be appreciated that any suitable electrical coupling or powersource is contemplated.

Sequential tube dilation systems can utilize sequential dilation of apercutaneous tissue opening with successively larger diameter dilatorsto access a surgical site in order to limit collateral tissue damage.

FIGS. 5A and 5B illustrate one version of a circumferential multi-polargrid array associated with a tissue dilator system 20. The orientationlines 132 on the dilator system 20 can be the same as described withrespect to the multi-polar surgical probe 18. The grid array 130utilized on the tissue dilator system 20 can generally be the same asthe multi-polar surgical probe 18 except that the 1st row of electrodes133 on the tissue dilator system 20 can contain multiple electrodes 131in comparison to the multi-polar surgical probe 18 which may contains asingle electrode in row #1 at the distal tip of the surgical probe 18.An electrical ring connector 50 can be used to couple the electricalpower source of the multi-polar stimulation unit 16 to the gridelectrode array 131. The electrical ring connector can be coupled to themulti-polar stimulation unit 16 with a wire 60, or any other suitableconnection. Referring to FIG. 5B, the electrical ring connector 50 caninclude an annular band 161 having a plurality of projections 162 thatcan be configured to engage a plurality of corresponding slots 164 inthe dilator system 20.

FIGS. 6A-6B illustrate an example of three different sizes of tubedilator systems 20, 120, 220 that can be used for sequential dilationwith the largest diameter dilator system 20, a medium size dilatorsystem 220 and a small diameter dilator 120. The dilator system 20 canbe associated with the electrical ring connector 50, the medium sizedilator system 220 can be associated with an electrical ring connector250, and the small diameter dilator 120 can be associated with anelectrical ring connector 150.

FIGS. 7A and 7B illustrate one version of how a surgical sequentialdilation system can include multiple tube dilators 20, 120, 220positioned over one another to sequentially create a surgical corridorfollowing confirmation of the correct initial positioning andconfirmation of safe access with the multi-polar surgical probe 18. Eachsequentially larger size dilator system 20, 120, 220 can slide easilyover a smaller diameter tube dilator system or probe 18. The tubedilator systems 20, 120, 220 can also define a hollow lumen that canallow access for surgical instruments once a corridor is created.

Referring to FIG. 8, one example of a connection for the electricalpower source of the multi-polar stimulation unit 16 to the dilator 20can be to use an electrical ring connector 50. The electrical ringconnector 50 can have a female-type electrical input port 166 that canbe configured to receive a removable electrical plug connector 168 withmale type electrical pin connectors. The removable electrical plugconnector 166 can fit into all the different diameter ring connectors50, 150, 250, for example. FIG. 8 illustrates one version of theelectrical ring connector 50. The inferior portion of the ring connector50 can be fitted with electrical male type electrical contacts 162 toconnect the electrical wiring with female ports 164 in the dilatorsystem 20. These connections can electrically couple the electrical ringconnector 50 to the electrical wiring 46 of the tube dilator system 20and can deliver current to each electrode 31 on the electrical grid 30without restricting functionality. An orientation line on the ringelectrode connector can be utilized to properly align the ringconnectors with the correct electrical contacts. This ring connectorsystem is only an example of how to design an electrical connection fromthe power source of the multi-polar stimulation unit 16 to theelectrical grid 30 without interfering with the functionality of thedilator systems 20, 120, 220. Any other suitable designs orconfigurations of electrical connections can be utilized.

FIG. 9 illustrates one version of how the electrical grid 30 can bewired on the multi-polar dilator system 20. Each electrode 31 can beelectrically wired 46 directly and independently of the other electrodesto provide precisely controlled, focal electrical stimulation to eachelectrode on the grid 30 as is described in the section on multi-polarelectrical stimulation sequencing of peripheral nerves/roots withsequential motor thresholding using circumferential and planar gridarrays.

Referring to FIG. 10, surgical retractor systems can create and maintaina surgical corridor to access deep surgical target sites. In oneversion, a multi-polar sequencing grid array applied to a surgicalretractor system can assist in providing safe surgical access, mappingof neural structures within the surgical field, and/or continuousfunctional neuromonitoring throughout a surgical procedure.

Similar principles that have been described for multi-polar stimulationin a circumferential grid array for the multi-polar surgical probe andthe multi-polar tube dilation system can be applied to a planar gridarray (a single plane of stimulating surface as opposed to 360° ofstimulating on the circumferential grid array). In the planarconfiguration, the grid electrode array can be fixed on the surface of ablade of a surgical retractor where, for example. FIG. 10 illustrates aretractor system 22 that can be fitted with a multi-polar grid 330electrode system comprises of electrodes 331 on the primary retractorblade. The base unit of the retractor system 22 can accept four separateremovable retractor blades 370, 371, 372, 373, which can be movedindependently to create a surgical corridor. In the example illustrationprovided, only the primary retractor blade 370 can be outfitted with amulti-polar grid 330 array system for the same of simplicity, however,in practice any or all of the retractor blades can be fitted with amulti-polar grid array. In one example of the retractor system 22, therecan be four retractor blades. A primary or anterior retractor blade 370with the grid 330 electrode blade 370, two lateral retractor blades 371,372 and a secondary or posterior retractor blade 373 can be included. Aremovable electrical pin connector 374 can be attached to an electricalpower cord 360 to couple the electrical power source of the multi-polarstimulation unit 16 to the multi-polar grid 330 on the primary retractorblade 370 via an electrical port connection 375 that can be located atthe top of the retractor blade. This can be seen in more detail in FIGS.11A-C which illustrate one version of the primary retractor blade 370along with a schematic of the electrical wiring 346 and connections 374,375 which can connect the multi-polar stimulation unit 16 to power thegrid 330 electrode array. The magnified area shows how these connectionscan utilize a typical male-female electrical contact connector that canbe located at the top of the retractor blade 370.

Referring to FIG. 12, The designation of alphanumeric names to eachparticular electrode 331 can direct the software to control the deliveryof precisely controlled electrical stimulation from the multi-polarstimulation unit 16 (FIG. 11B) independently to each electrode on thegrid 330 as is described in greater detail in the section on multi-polarelectrical stimulation sequencing of peripheral nerves/roots withsequential motor thresholding using circumferential and planar gridarrays.

In an example planar electrode grid arrangement, the electrodes 331 canhave, for example, designated names alphanumerically in a left to rightand inferior to superior fashion. The planar grid can be arranged intorows and columns. In the current illustration, there are three columns(A, B & C) which can designate the horizontal position of the electrode331 in each row which include column A (left column), column B (middlecolumn) and column C (right column). The rows can designate the verticalposition of the electrode 331 with the most distal electrodes 331 (row#1) being located in the distal end of the retractor blade 370. In theillustrated example, there are seven rows (1-7) with row #1 at the mostdistal tip of the retractor with subsequent numbering proceedingsuperiorly towards the base of the retractor. The 1A electrode can belocated in the left distal end of the retractor. Each row (1-7) can havethree electrodes (A, B & C) as is shown in FIG. 11A. It will beappreciated that any suitable number of electrodes having any suitableconfiguration or nomenclature are contemplated. The electrodes can beequally spaced apart, can have non-uniform spacing, can be concentratedin suitable areas, or can otherwise be suitably configured.

Referring to FIGS. 14A and 14B, an example embodiment of a systemintegrating multiple components is shown. It will be appreciated thatany suitable arrangement, number, and configuration of components iscontemplated.

With multi-polar sequential electrical stimulation with a grid array thesize, shape, and intensity of the electrical fields can be altered byvarying the current delivered to each particular electrode on the gridarray. By selecting electrode configurations, currents/voltages andpulse widths, regions of the anatomy surrounding the stimulatingelectrodes that are electrified can be controlled. By recording evokedEMG responses from stimulation of various sets of electrodes on thegrid, information can be obtained about the presence, direction,proximity and functional status of neural structures in the surgicalfield. Software can control the delivery of electrical current tovarious sets of electrodes in the grid and can simultaneously record anyevoked motor EMG activity. The sets of electrodes that evoke motorresponses can provide information about the presence of neuralstructures within the surgical field. Conversely, the absence of anyevoked EMG responses (up to predetermined maximum stimulus intensity)can suggest an absence of motor neural structures within the areasurrounding the stimulating electrodes. If stimulation of a particularset of electrodes on the grid evokes a motor response while other setsof electrodes do not, information can be deduced about the direction ofneural structures within the surgical field in relation to thestimulating electrodes. By thresholding any evoked motor responses(calculating the minimum amount of electrical current required to elicita motor response), information can be deduced about the proximity of theneural structures. Information about the proximity of neural structurescan be based on the general understanding that neural elements in closeproximity to the stimulating electrodes will elicit motor responses at alower amount of electrical stimulus intensity (measured in milliamps)and neural elements that are relatively more distant will require agreater amount of current to elicit a motor response. A motor threshold“map” can be generated by the software and displayed after multiplesequential stimulations are delivered to various sets of electrodes onthe grid.

Electrode grid design and software programming can constrain theelectrical fields to control which regions of the surgical field areelectrified at any given time. The stimulus timing, waveform shape andelectrode polarity can create focal electrical fields for accurate motorfiber monitoring and mapping. The shape and distribution of theelectrical fields created by the electrical current/voltage can bestrategically controlled. The size, shape and gradient or intensity ofan electrical field can be affected by the configuration of the gridelectrodes and which electrodes are activated at any given time.

Multiple electrode configurations have been commonly utilized in otherdisciplines including cardiac pacing, FES (Functional ElectricalStimulation for muscle deprived of nervous control to providing muscularcontraction and producing a functionally useful moment), DBS (Deep BrainStimulation-implantation of electrodes for therapeutic control ofmovement disorders and chronic pain), SCS (Spinal Cord Stimulation-forcontrol of chronic pain) and cochlear implants.

The software of versions herein can be designed to provide the abilityto assign electrical polarity to each particular electrode on the grid.Activation of any electrode on the grid (or combinations of electrodes)with a particular assignment of polarity can result in the ability tocreate various combinations of shapes, sizes and spatial distributionsof electrical fields. The configurability and re-configurability of thegrid electrodes between successive stimulations can provide the abilityto assign varied polarities and stimulation parameters to alter thegenerated electrical fields and thus scan the surgical field for motorevoked responses.

In addition, the software can have the ability to activate multipleelectrodes in the grid simultaneously and can assign particularpolarities to each of them. Activation of multiple electrodessimultaneously with varied polarities is sometimes referred to as“current steering” and can be used to increase the selectivity of agiven configuration of electrodes by activating tissue that could not beactivated by driving the electrodes independently.

This ability to assign polarities and stimulus parameters to one ormultiple electrodes on the grid can allow the multi-polar grid arraysystem to utilize multiple stimulation paradigms to vary the size, shapeand distributions of the electrical fields (mono-polar, bipolar,tripolar, etc.). The software program can be varied to deliver specifictypes of stimulation or sequences of stimulations according to thesurgical situation and the particular monitoring/mapping requirements.

FIGS. 15A-17D illustrate example stimulation paradigms for multi-polarplanar grid electrode arrays. FIG. 15A illustrates one version ofmono-polar stimulation where the system 422 can include only a singlecathode (negative) electrode 480 activated on the grid 430. Inmono-polar stimulation, the return electrode or anode 481 (positive) canplaced at some distance away from the cathode 480. The electrical fieldlines can emit radially outward from the source of the current, thecathode (−), and the return current at the anode (+) can be placed at adistant site. Mono-polar stimulation can be more useful in someparticular situations when sensitivity is forever over specificity.

FIGS. 15C and 15D also illustrate examples of bipolar stimulation. In abipolar stimulation configuration, current can travel from one electrode(a cathode 480 or negative electrode) to another peripheral electrode(an anode 481 or positive electrode). With bipolar stimulation, theelectrical charge can flow from the negative cathode 480 to the positiveanode 481 as shown by the electrical field lines. This results can be amore focused, localized stimulation. Bi-polar stimulation can result inless current spread than mono-polar stimulation and therefore smaller,more selective activation.

Bipolar stimulation can be delivered by designating any two electrodeson this grid as a cathode 480 and anode 481, for example. FIGS. 15C and15D illustrate 2 two different electrical fields that can be generatedwith bi-polar stimulation when different electrodes are assigned as thecathode 480 and anode 481. In one example, as shown in FIG. 15C, thecathode 480 is assigned to electrode 5B while the anode 481 is assignedto electrode 4B. In FIG. 15D, the assigned polarities can be reversedwith the cathode 480 assigned to electrode 4B while the anode 481 can beassigned to electrode 5B.

FIGS. 16A-16C illustrate examples of different sub-types of bi-polarstimulation and how the distance between the two electrodes 480, 481 canhave significant effects on the size, shape and orientation of theinduced electrical fields. FIG. 16B represents one version of narrowbi-polar stimulation where there can be a short distance between thecathode 480 (electrode 5B) and anode 481 (electrode 4B) that can resultin a localized, focal electrical field. In a wider bi-polarconfiguration, as illustrated in FIG. 16C, there can be a greaterdistance between the cathode 480 (electrode 5B) and anode 481 (3B) whichcan result in a larger current distribution. In this instance, there canbe an inactive electrode 482 (4B) which can separate the cathode 480(5B) and anode 481 (3B).

FIGS. 17A-C illustrate examples of tri-polar stimulation systems 422where a single cathode 480 can be active and can send current to a firstanode 481 and a second anode 483 that can share an equal potentialdifference. Tri-polar stimulation may be beneficial because it can moreeffectively localize the electrical field and limit the amount ofcurrent spread. In the example shown in FIG. 17B, the single cathode 480can be assigned to electrode 5B, and first and second anodes 481, 483can be assigned in a linear arrangement above and below the cathode at6B and 4B. In the example shown in FIG. 17C, there can be a singlecathode 480 that can be assigned to electrode 1A and first and secondanodes 481, 483 that can be positioned perpendicularly at 2A and 1B. Thetheoretical shapes of the electrical fields generated by both of thesetripolar arrangements are illustrated. Other tri-polar arrangements arepossible including wide tri-polar arrangements with a greater separatedistance between the cathode and anodes. Many other multipolar electrodeassignments can be envisioned with any combination of electrodeassignments including differing numbers of active anodes and cathodes.Certain combinations of electrode assignments may be found to be usefulin controlling the generated electrical fields to optimize nerve fiberlocalization in the surgical field. The optimal electrode assignmentsand sequencing of stimulations may be determined with mathematicalmodeling and experimental studies.

These examples of the different stimulation paradigms illustrate howvarious electrical fields can be created by systematically andstrategically assigning different polarities and stimulation schemes tovarious electrodes on the grid electrode array. By combining theinformation gained from multiple sequences of stimulations, a thresholdmap of the evoked responses can be obtained, which can localize thepresence of motor fibers in the surgical field in relation to the gridelectrodes. Mathematical modeling and/or experimental studies may guidethe software programming towards the optimal electrode polarityassignments and stimulation sequencing protocols that would map asurgical site most efficiently. An efficient stimulation sequence canthen quickly generate a color coded map that can be displayed to informthe surgeon of the location and proximity of neural structures locatedwithin the surgical field. Examples described herein can utilize theseunique systems and methods to improve the accuracy and resolution ofnerve mapping and can increase the surface area along the depth of theoperative corridor which can be mapped and monitored compared toexisting materials and methods of nerve monitoring and mapping.

In general, it will be apparent to one of ordinary skill in the art thatat least some of the embodiments described herein can be implemented inmany different embodiments of software, firmware, and/or hardware. Thesoftware and firmware code can be executed by a processor or any othersimilar computing device. The software code or specialized controlhardware that can be used to implement embodiments is not limiting. Forexample, embodiments described herein can be implemented in computersoftware using any suitable computer software language type, using, forexample, conventional or object-oriented techniques. Such software canbe stored on any type of suitable computer-readable medium or media,such as, for example, a magnetic or optical storage medium. Theoperation and behavior of the embodiments can be described withoutspecific reference to specific software code or specialized hardwarecomponents. The absence of such specific references is feasible, becauseit is clearly understood that artisans of ordinary skill would be ableto design software and control hardware to implement the embodimentsbased on the present description with no more than reasonable effort andwithout undue experimentation.

Moreover, the processes described herein can be executed by programmableequipment, such as computers or computer systems and/or processors.Software that can cause programmable equipment to execute processes canbe stored in any storage device, such as, for example, a computer system(nonvolatile) memory, an optical disk, magnetic tape, or magnetic disk.Furthermore, at least some of the processes can be programmed when thecomputer system is manufactured or stored on various types ofcomputer-readable media.

It can also be appreciated that certain portions of the processesdescribed herein can be performed using instructions stored on acomputer-readable medium or media that direct a computer system toperform the process steps. A computer-readable medium can include, forexample, memory devices such as diskettes, compact discs (CDs), digitalversatile discs (DVDs), optical disk drives, or hard disk drives. Acomputer-readable medium can also include memory storage that isphysical, virtual, permanent, temporary, semi-permanent, and/orsemi-temporary.

A “computer,” “computer system,” “host,” “server,” or “processor” canbe, for example and without limitation, a processors, microcomputer,minicomputer, server, mainframe, laptop, personal data assistant (PDA),wireless e-mail device, cellular phone, pager, processors, fax machine,scanner, or any other programmable device configured to transmit and/orreceive data over a network. Computer systems and computer-based devicesdisclosed herein can include memory for storing certain software modulesused in obtaining, processing, and communicating information. It can beappreciated that such memory can be internal or external with respect tooperation of the disclosed embodiments. The memory can also include anymeans for storing software, including a hard disk, an optical disk,floppy disk, ROM (read only memory), RAM (random access memory), PROM(programmable ROM), EEPROM (electrically erasable PROM) and/or othercomputer-readable media. Non-transitory computer-readable media, as usedherein, comprises all computer-readable media except for a transitory,propagating signals.

In various embodiments disclosed herein, a single component can bereplaced by multiple components and multiple components can be replacedby a single component to perform a given function or functions. Exceptwhere such substitution would not be operative, such substitution iswithin the intended scope of the embodiments. The computer systems cancomprise one or more processors in communication with memory (e.g., RAMor ROM) via one or more data buses. The data buses can carry electricalsignals between the processor(s) and the memory. The processor and thememory can comprise electrical circuits that conduct electrical current.Charge states of various components of the circuits, such as solid statetransistors of the processor(s) and/or memory circuit(s), can changeduring operation of the circuits.

Some of the figures can include a flow diagram. Although such figurescan include a particular logic flow, it can be appreciated that thelogic flow merely provides an exemplary implementation of the generalfunctionality. Further, the logic flow does not necessarily have to beexecuted in the order presented unless otherwise indicated. In addition,the logic flow can be implemented by a hardware element, a softwareelement executed by a computer, a firmware element embedded in hardware,or any combination thereof.

The foregoing description of embodiments and examples has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or limiting to the forms described. Numerous modificationsare possible in light of the above teachings. Some of thosemodifications have been discussed, and others will be understood bythose skilled in the art. The embodiments were chosen and described inorder to best illustrate principles of various embodiments as are suitedto particular uses contemplated. The scope is, of course, not limited tothe examples set forth herein, but can be employed in any number ofapplications and equivalent devices by those of ordinary skill in theart. Rather it is hereby intended the scope of the invention to bedefined by the claims appended hereto.

1. (canceled)
 2. A nerve mapping system comprising: a computer systemconfigured to: cause delivery of sequential variable multi-polarstimulation to electrodes of a grid array of electrodes according to aplurality of stimulation configurations to scan the grid array andelicit evoked potential responses, wherein the plurality of stimulationconfigurations include at least mono-polar, bi-polar, and tri-polarstimulation configurations of different electrodes of the grid array,and wherein the electrodes are positioned on a surface of an instrumentinserted into a tissue site of a patient to map locations andproximities of neural structures in the tissue site; and receive theevoked potential responses and combine information gathered based on theevoked potential responses to enable nerve mapping.
 3. The nerve mappingsystem of claim 2, wherein each of the electrodes is configured to bestimulated individually and independently, and wherein every one of theelectrodes is configured to be stimulated as part of at leastmono-polar, bi-polar, and tri-polar stimulation configurations.
 4. Thenerve mapping system of claim 2, wherein the computer system is furtherconfigured to: generate a virtual map of locations and proximities ofneural structures in the tissue site based at least in part on theinformation gathered based on the evoked potential responses.
 5. Thenerve mapping system of claim 4, wherein the virtual map includes: agraphical representation of the instrument including a graphicalrepresentation of the grid array and the positions of the electrodes ofthe grid array overlaid on the graphical representation of theinstrument; and one or more colors overlaid on the graphicalrepresentation of the instrument including the graphical representationof the grid array of electrodes, wherein the one or more colors indicatethe locations and proximities of the neural structures in relation tothe instrument and to each electrode of the grid array of electrodes onthe surface of the instrument.
 6. The nerve mapping system of claim 4,wherein the computer system is further configured to: output the virtualmap for display on an electronic display.
 7. The nerve mapping system ofclaim 2, wherein the instrument comprises at least one of: a probe, atissue dilator, or a retractor system.
 8. The nerve mapping system ofclaim 2, wherein the instrument comprises a probe for peripheral nervemapping.
 9. The nerve mapping and monitoring system of claim 2, whereinthe instrument comprises a combination of a retractor system, aplurality of tissue dilators, and a probe, and wherein each of theretractor system, the plurality of tissue dilators, and the probeincludes at least a portion of the grid array of electrodes.
 10. Thenerve mapping system of claim 2, wherein the computer system is furtherconfigured to: adjust one or more stimulation parameters when causingdelivery of stimulation to electrodes of the grid array, wherein the oneor more stimulation parameters include at least one of: current level,voltage level, or pulse width.
 11. An apparatus for nerve mapping, theapparatus comprising: an instrument configured to be inserted into atissue site of a patient; and a grid array of a plurality of electrodespositioned on a surface of the instrument and configured to enablemapping of locations and proximities of neural structures in the tissuesite, wherein: each of the plurality of electrodes is configured to bestimulated individually and independently according to a plurality ofstimulation configurations to scan the grid array and elicit evokedpotential responses, and every one of the plurality of electrodes isconfigured to be stimulated as part of at least mono-polar, bi-polar,and tri-polar stimulation configurations of different electrodes of thegrid array.
 12. The apparatus of claim 11, wherein the plurality ofstimulation configurations involve delivery of sequential variablemulti-polar stimulation to electrodes of the grid array.
 13. Theapparatus of claim 11, wherein the instrument comprises at least one of:a surgical probe, a tissue dilator, or a retractor system.
 14. Theapparatus of claim 11, wherein the instrument comprises a probe forperipheral nerve mapping.
 15. The apparatus of claim 11, wherein thesurgical instrument comprises a combination of a retractor system, aplurality of tissue dilators, and a surgical probe, and wherein each ofthe retractor system, the plurality of tissue dilators, and the surgicalprobe includes at least a portion of the grid array.
 16. The apparatusof claim 11, wherein the grid array comprises and arrangement of theelectrodes on the surface of the instrument in a plurality of rows and aplurality of columns.
 17. The apparatus of claim 11 further comprising:one or more recording electrodes or needles configured to detect evokedpotential responses elicited by stimulation of combinations ofelectrodes of the grid array according to the plurality of stimulationconfigurations.
 18. A method of nerve mapping, the method comprising:providing an apparatus for nerve mapping according to claim 11;inserting the instrument, including the grid array, into a tissue siteof a patient; and initiating delivery of sequential variable multi-polarstimulation to electrodes of the grid array according to a plurality ofstimulation configurations to scan the grid array and elicit evokedpotential responses to provide nerve mapping.
 19. The method of claim 18further comprising: causing display of a virtual map of locations andproximities of neural structures in the tissue site, wherein is virtualmap is generated based at least in part on information gathered based onthe evoked potential responses.
 20. The method of claim 19, wherein thevirtual map includes: a graphical representation of the instrumentincluding a graphical representation of the grid array and the positionsof the electrodes of the grid array overlaid on the graphicalrepresentation of the instrument; and one or more colors overlaid on thegraphical representation of the instrument including the graphicalrepresentation of the grid array, wherein the one or more colorsindicate the locations and proximities of the neural structures inrelation to the instrument and to each electrode of the grid array onthe surface of the instrument.
 21. The method of claim 18, wherein theinstrument comprises at least one of: a probe for peripheral nervemapping, a tissue dilator, a retractor system, or a combination of aretractor system, a plurality of tissue dilators, and a probe, andwherein each of the retractor system, the plurality of tissue dilators,and the probe of the combination includes at least a portion of the gridarray.